Presence detecting devices, including such devices for automatic doors, have been heretofore known and/or utilized wherein a plurality of infrared emitters and receivers are utilized to provide a detection area, for example in a security area or at the threshold of the automatically actuated door (see for example U.S. Pat. Nos. 4,179,691, 4,823,010, 4,733,081, 4,697,383, 4,669,218, 4,565,029, and 4,698,937). In general, such devices have utilized single clock synchronization of infrared emitters to project a beam of energy in a detection area and receivers together with detector circuitry to receive reflected energy and send an operational signal when a target is detected at or near the threshold of a door.
Various arrangements to compensate for variations in environmental factors in the detection area to minimize the number of malfunctions, or detection errors, are also known and/or have been utilized (see, for example, U.S. Pat. Nos 4,929,833, 4,570,157, and 4,119,843). Such arrangements include manual threshold sensitivity adjustments (see for example U.S. Pat. No. 4,823,010) and/or utilization of elaborate and expensive multiple integration circuits (see for example U.S. Pat. No. 4,733,081, wherein the rate of change, or variation, of signal is utilized to discriminate a human body from the background signal received by a detector).
While, in some cases, heretofore known devices have employed means to prevent systematic detection errors, such as the door itself being operationally treated as a target (for example by turning off the sensor or eliminating sensor signal response during door operation), or malfunction or error caused by in housing light transmission, such devices have not proven entirely successful in eliminating such malfunction or false triggers, for example resulting in opening of a door where no body, such as a human body, shopping cart or the like, is present, or failure to open when a body is present.
It would thus be desirable to provide a simple and inexpensive presence detecting apparatus which includes automatic adjustment of the sensitivity of such an apparatus to compensate for changes in the environment in a detection area (such as snowfall, rain, daylight and darkness), while providing means for ignoring systematic occurrences, such as door movement, light transmission inside of the apparatus housing, and the like, and/or random and short lived transient occurrences. Further improvement in such heretofore known devices and methods could thus still be utilized.